In inflamed airway, changes in epithelial architecture, matrix, glands, and vessels promote obstruction and hypersecretion in chronic bronchitis and asthma. This project tests the hypothesis that peptidases control resolution of remodeling and other aspects of chronic airway inflammation. It uses novel approaches such as targeting peptidases in living cells with activity-based probes, probing immune cell interactions with real time imaging in mouse models of chronic infection, and exploring contributions of genetic variation in mast cell peptidases to human asthma. Aim 1 is to determine roles of the airway epithelial peptidase prostasin in chronic infection. Epithelial integrity and hydration is essential for defense against microbes and toxins. Failure of barrier function leads to chronic infection and remodeling, as in cystic fibrosis. Aim 1 studies test the hypothesis that prostasin support of airway ion flux and integrity is controlled by membrane anchoring, activation, inhibition and shedding. Aim 2 is to determine roles of mast cell peptidases in resolving inflammation. Mast cell products can Inflict harm, but mouse studies suggest they also promote survival from septic peritonitis and pneumonia. By helping to resolve infection, their overall effect can be anti-inflammatory. Aim 2 studies test the hypothesis that mast cell peptidases promote resolution of chronic inflammation. Aim 3 is to determine impact of mast cell tryptase deficiency on chronic airway inflammation. Tryptases are implicated in airway remodeling in allergic and autoimmune inflammation and in defense against bacterial infection and thus have the potential to produce as well as to resolve inflammation. Our recent work reveals that dysfunctional human tryptases are common and that Individuals and populations vary strikingly in number of active tryptase genes inherited. By exploring connections between genotype and asthma, a disease associated not only with chronic inflammation but with exacerbation by infection, the proposed studies test the hypothesis that differences in tryptase genotype contribute to inherited variation in asthma severity and susceptibility. Overall, the proposed studies are expected to identify mechanisms that suggest previously unexplored strategies to prevent or reverse the pathology of chronic airway inflammation.